Buggy code:
Font regularFont ; Font boldFont ; Font italicFont ; Font boldItalicFont ; int tabWidth ; int ascent ; int descent ; int lineEndSpaceWidth ; int averageCharWidth ; int topIndex = - 1 ; TextLayout [ ] layouts ; int lineCount ; int [ ] lineWidth ; int [ ] lineHeight ; StyledTextRenderer . LineInfo [ ] lines ; int maxWidth ; int maxWidthLineIndex ; boolean idleRunning ; int [ ] ranges ; int styleCount ; StyleRange [ ] styles ; static final int GROW = 32 ; static final int IDLE_TIME = 50 ; static final int CACHE_SIZE = 128 ; static final int BACKGROUND = 1 << 0 ; static final int ALIGNMENT = 1 << 1 ; static final int INDENT = 1 << 2 ; static final int JUSTIFY = 1 << 3 ; static final int BULLET = 1 << 4 ; static final int SEGMENTS = 1 << 5 ; class LineInfo { int flags ; Color background ; int alignment ; int indent ; boolean justify ; Bullet bullet ; int [ ] segments ; public LineInfo ( ) { } public LineInfo ( StyledTextRenderer . LineInfo info ) { } } StyledTextRenderer ( Device device , StyledText styledText ) { } void calculate ( int startLine , int lineCount ) { } void calculateClientArea ( ) { } void calculateIdle ( ) { } void clearLineBackground ( int startLine , int count ) { } void clearLineStyle ( int startLine , int count ) { } void copyInto ( StyledTextRenderer renderer ) { } void dispose ( ) { } void disposeTextLayout ( TextLayout layout ) { } int drawLine ( int lineIndex , int paintX , int paintY , GC gc , Color widgetBackground , Color widgetForeground ) { } int getBaseline ( ) { } Font getFont ( int style ) { } FontData [ ] getFontData ( int style ) { } int getHeight ( ) { } int getLineAlignment ( int index , int defaultAlignment ) { } Color getLineBackground ( int index , Color defaultBackground ) { } Bullet getLineBullet ( int index , Bullet defaultBullet ) { } int getLineEndSpace ( ) { } int getLineHeight ( ) { } int getLineHeight ( int lineIndex ) { } int getLineIndent ( int index , int defaultIndent ) { } boolean getLineJustify ( int index , boolean defaultJustify ) { } int [ ] getLineSegments ( int index , int [ ] defaultSegments ) { } int getRangeIndex ( int offset , int low , int high ) { } int [ ] getRanges ( int start , int length ) { } StyleRange [ ] getStyleRanges ( int start , int length , boolean includeRanges ) { } StyleRange getStyleRange ( StyleRange style ) { } TextLayout getTextLayout ( int lineIndex ) { } TextLayout getTextLayout ( int lineIndex , int orientation , int width , int lineSpacing ) { } int getWidth ( ) { } void reset ( ) { } void reset ( int startLine , int lineCount ) { } void setContent ( StyledTextContent content ) { } void setFont ( Font font , int tabs ) { TextLayout layout = new TextLayout ( device ) ; layout . setFont ( regularFont ) ; <START_BUG> if ( ( font != null ) && ( ! ( font . equals ( regularFont ) ) ) ) { <END_BUG> if ( ( boldFont ) != null ) boldFont . dispose ( ) ; if ( ( italicFont ) != null ) italicFont . dispose ( ) ; if ( ( boldItalicFont ) != null ) boldItalicFont . dispose ( ) ; boldFont = italicFont = boldItalicFont = null ; regularFont = font ; layout . setText ( "<seq2seq4repair_space>" ) ; layout . setFont ( font ) ; layout . setStyle ( new TextStyle ( getFont ( NORMAL ) , null , null ) , 0 , 0 ) ; layout . setStyle ( new TextStyle ( getFont ( BOLD ) , null , null ) , 1 , 1 ) ; layout . setStyle ( new TextStyle ( getFont ( ITALIC ) , null , null ) , 2 , 2 ) ; layout . setStyle ( new TextStyle ( getFont ( ( ( SWT . BOLD ) | ( SWT . ITALIC ) ) ) , null , null ) , 3 , 3 ) ; FontMetrics metrics = layout . getLineMetrics ( 0 ) ; ascent = ( metrics . getAscent ( ) ) + ( metrics . getLeading ( ) ) ; descent = metrics . getDescent ( ) ; lineEndSpaceWidth = layout . getBounds ( 0 , 0 ) . width ; boldFont . dispose ( ) ; italicFont . dispose ( ) ; boldItalicFont . dispose ( ) ; boldFont = italicFont = boldItalicFont = null ; } StringBuffer tabBuffer = new StringBuffer ( tabs ) ; for ( int i = 0 ; i < tabs ; i ++ ) { tabBuffer . append ( '<seq2seq4repair_space>' ) ; } layout . setText ( tabBuffer . toString ( ) ) ; tabWidth = layout . getBounds ( ) . width ; layout . dispose ( ) ; } void setLineAlignment ( int startLine , int count , int alignment ) { } void setLineBackground ( int startLine , int count , Color background ) { } void setLineBullet ( int startLine , int count , Bullet bullet ) { } void setLineIndent ( int startLine , int count , int indent ) { } void setLineJustify ( int startLine , int count , boolean justify ) { } void setLineSegments ( int startLine , int count , int [ ] segments ) { } void setStyleRanges ( int [ ] newRanges , StyleRange [ ] newStyles ) { } int addMerge ( StyleRange [ ] mergeStyles , int mergeCount , int modifyStart , int modifyEnd ) { }

Fix:
if ( font != ( regularFont ) ) {